Software Engineering

Transcription

1 Software Engineering Object-Oriented Analysis and Design and Modeling with UML Assoc. Prof. Marenglen Biba MSc in Computer Science, UoG-UNYT Foundation Programme 3-1

2 Material Get the material from Sufficient for FP exam purposes Other useful material I. Sommerville. Software Engineering (in library) R. Pressman. Software Engineering: A Practitioner's Approach (in library) B. Bruegge & A. H. Dutoit. Object-Oriented Software Engineering: Using UML, Patterns, and Java, 2nd Edition.

3 Requirements Analysis and UML Abstraction and Modeling Decomposition Hierarchy Object-Oriented Modeling UML Diagrams Use case diagrams Case study in lab

4 What is the problem with this Drawing?

5 Abstraction Complex systems are hard to understand The phenomena Our short term memory cannot store more than 7+-2 pieces at the same time -> limitation of the brain My Phone Number:

6 Abstraction Complex systems are hard to understand The phenomena Chunking: Our short term memory cannot store more than 7+-2 pieces at the same time -> limitation of the brain My Phone Number: Group collection of objects to reduce complexity 4 chunks: State-code, Area-code, Local-Prefix, Internal-Nr

7 Abstraction Complex systems are hard to understand The phenomena Chunking: Our short term memory cannot store more than 7+-2 pieces at the same time -> limitation of the brain My Phone Number: Group collection of objects to reduce complexity State-code, Area-code, Local Prefix, Internal-Nr Phone Number Country-Code Area-Code Local-Prefix Internal-Nr

8 We use Models to describe Software Systems Object model: What is the structure of the system? Functional model: What are the functions of the system? Dynamic model: How does the system react to external events? System Model: Object model + functional model + dynamic model

9 Technique to deal with Complexity: Decomposition A technique used to master complexity ( divide and conquer ) Two major types of decomposition Functional decomposition Object-oriented decomposition Functional decomposition The system is decomposed into modules Each module is a major function in the application domain Modules can be decomposed into smaller modules.

10 Decomposition (cont d) Object-oriented decomposition The system is decomposed into classes ( objects ) Each class is a major entity in the application domain Classes can be decomposed into smaller classes

11 Class Identification Basic assumptions: We can find the classes for a new software system: Greenfield Engineering We can identify the classes in an existing system: Reengineering We can create a class-based interface to an existing system: Interface Engineering.

12 Hierarchy So far we got abstractions This leads us to classes and objects Chunks Another way to deal with complexity is to provide relationships between these chunks One of the most important relationships is hierarchy 2 special hierarchies "Part-of" hierarchy "Is-kind-of" hierarchy.

13 Part-of Hierarchy (Aggregation) Computer I/O Devices CPU Memory Cache ALU Program Counter

14 Is-Kind-of Hierarchy (Taxonomy) Cell Muscle Cell Blood Cell Nerve Cell Striate Smooth Red White Cortical Pyramidal

15 Where are we? Three ways to deal with complexity: Abstraction, Decomposition, Hierarchy Object-oriented decomposition is good Unfortunately, depending on the purpose of the system, different objects can be found How can we do it right? Start with a description of the functionality of a system Then proceed to a description of its structure Ordering of development activities Software lifecycle

16 Requirements Elicitation UML diagrams Case Study: Use case diagrams with UML 7-16

17 Software Lifecycle Activities Requirements Elicitation Analysis System Design Detailed Design Implementation Testing Expressed in terms of Structured by Realized by Implemented by Verified By Use Case Model Application Domain Objects Subsystems Solution Domain Objects class... class... class... Source Code? class...? Test Case Model

18 First step in identifying the Requirements: System identification Two questions need to be answered: 1. How can we identify the purpose of a system? What are the requirements, what are the constraints? 2. What is inside, what is outside the system? These two questions are answered during requirements elicitation and analysis Requirements elicitation: Definition of the system in terms understood by the customer and/or user ( Requirements specification ) Analysis: Definition of the system in terms understood by the developer (Technical specification, Analysis model ) Requirements Process: Consists of the activities Requirements Elicitation and Analysis.

19 Techniques to elicit Requirements Bridging the gap between end user and developer: Questionnaires: Asking the end user a list of preselected questions Task Analysis: Observing end users in their operational environment Scenarios: Describe the use of the system as a series of interactions between a specific end user and the system Use cases: Abstractions that describe a class of scenarios. Job: Software Analyst, Business Analyst

20 What is UML? UML (Unified Modeling Language) Nonproprietary standard for modeling software systems, OMG Convergence of notations used in object-oriented methods OMT (James Rumbaugh and collegues) Booch (Grady Booch) OOSE (Ivar Jacobson) Current Version: UML 2.2 Information at the OMG portal Commercial tools: Rational (IBM),Together (Borland), Visual Architect (business processes, BCD) Open Source tools: ArgoUML, StarUML, Umbrello Commercial and Opensource: PoseidonUML (Gentleware)

21 What is UML? Unified Modeling Language Convergence of different notations used in object-oriented methods, mainly OMT (James Rumbaugh and collegues), OOSE (Ivar Jacobson), Booch (Grady Booch) They also developed the Rational Unified Process, which became the Unified Process in year at GE Research, where he developed OMT, joined (IBM) Rational in 1994, CASE tool OMTool At Ericsson until 1994, developed use cases and the CASE tool Objectory, at IBM Rational since 1995, Developed the Booch method ( clouds ), ACM Fellow 1995, and IBM Fellow com/

22 UML Basic Notation: First Summary UML provides a wide variety of notations for modeling many aspects of software systems Models: Functional model: Use case diagrams Object model: Class diagrams Dynamic model: Sequence diagrams, statechart diagram

23 UML: First Pass You can solve 80% of the modeling problems by using 20 % UML We teach you those 20% rule: Pareto principle Vilfredo Pareto, Introduced the concept of Pareto Efficiency, Founder of the field of microeconomics.

24 UML First Pass Use case diagrams Describe the functional behavior of the system as seen by the user Class diagrams Describe the static structure of the system: Objects, attributes, associations Sequence diagrams Describe the dynamic behavior between objects of the system Statechart diagrams Describe the dynamic behavior of an individual object Activity diagrams Describe the dynamic behavior of a system, in particular the workflow.

25 UML Core Conventions All UML Diagrams denote graphs of nodes and edges Nodes are entities and drawn as rectangles or ovals Rectangles denote classes or instances Ovals denote functions Names of Classes are not underlined SimpleWatch Firefighter Names of Instances are underlined mywatch:simplewatch Joe:Firefighter An edge between two nodes denotes a relationship between the corresponding entities

26 UML first pass: Use case diagrams Classifier Use Case Actor. System boundary Use case diagrams represent the functionality of the system from user s point of view

27 UML first pass: Class diagrams Association Class Multiplicity 2 PushButton SimpleWatch Display Battery Time Class diagrams represent the structure of the system

28 UML first pass: Class diagrams Class diagrams represent the structure of the system Association Class Multiplicity 2 PushButton state push() release() Attribute 1 1 LCDDisplay blinkidx blinkseconds() blinkminutes() blinkhours() stopblinking() referesh() Watch Battery Load 1 Time Now Operations

29 Additional References Martin Fowler UML Distilled: A Brief Guide to the Standard Object Modeling Language, 3rd ed., Addison- Wesley, 2003 Grady Booch,James Rumbaugh,Ivar Jacobson The Unified Modeling Language User Guide, Addison Wesley, 2 nd edition, 2005 Open Source UML tools

30 Use case diagrams 7-30

31 Use case diagrams Use case diagrams Describe the functional behavior of the system as seen by the user Class diagrams Describe the static structure of the system: Objects, attributes, associations Sequence diagrams Describe the dynamic behavior between objects of the system Statechart diagrams Describe the dynamic behavior of an individual object Activity diagrams Describe the dynamic behavior of a system, in particular the workflow.

32 UML Use Case Diagrams Used during requirements elicitation and analysis to represent external behavior ( visible from the outside of the system ) Passenger PurchaseTicket An Actor represents a role, that is, a type of user of the system A use case represents a class of functionality provided by the system Use case model: The set of all use cases that completely describe the functionality of the system.

33 Actors Passenger Name An actor is a model for an external entity which interacts (communicates) with the system: User External system (Another system) Physical environment (e.g. Weather) An actor has a unique name and an optional description Examples: Optional Description Passenger: A person in the train GPS satellite: An external system that provides the system with GPS coordinates.

34 Use Case PurchaseTicket A use case represents a class of functionality provided by the system Use cases can be described textually, with a focus on the event flow between actor and system The textual use case description consists of 6 parts: 1. Unique name 2. Participating actors 3. Entry conditions 4. Exit conditions 5. Flow of events 6. Special requirements.

35 Textual Use Case Description Example Passenger PurchaseTicket 1. Name: Purchase ticket 2. Participating actor: Passenger 3. Entry condition: Passenger stands in front of ticket distributor Passenger has sufficient money to purchase ticket 4. Exit condition: Passenger has ticket 5. Flow of events: 1. Passenger selects the number of zones to be traveled 2. Ticket Distributor displays the amount due 3. Passenger inserts money, at least the amount due 4. Ticket Distributor returns change 5. Ticket Distributor issues ticket 6. Special requirements: None.

36 Uses Cases can be related Extends Relationship To represent seldom invoked use cases or exceptional functionality Includes Relationship To represent functional behavior common to more than one use case.

37 The <<extends>> Relationship <<extends>> relationships model exceptional or seldom invoked cases <<extends>> Passenger PurchaseTicket <<extends>> The exceptional event flows are factored out of the main event flow for clarity The direction of an <<extends>> relationship is to the extended use case Use cases representing exceptional flows can extend more than one use case. OutOfOrder <<extends>> <<extends>> TimeOut Cancel NoChange

38 The <<includes>> Relationship Passenger PurchaseSingleTicket <<includes>> <<extends>> PurchaseMultiCard CollectMoney <<extends>> <<includes>> <<includes>> relationship represents common functionality needed in more than one use case <<includes>> behavior is factored out for reuse, not because it is an exception The direction of a <<includes>> relationship is to the using use case (unlike the direction of the <<extends>> relationship). <<extends>> NoChange Cancel Cancel

39 Use Case Models can be packaged Classifier Use Case Actor. System boundary

40 Actor vs Class vs Object Actor An entity outside the system to be modeled, interacting with the system ( Passenger ) Class An abstraction modeling an entity in the application or solution domain The class is part of the system model ( User, Ticket distributor, Server ) Object A specific instance of a class ( Joe, the passenger who is purchasing a ticket from the ticket distributor ).

41 Class diagrams in UML: composition 7-41

42 Class diagrams in UML: inheritance 7-42

43 Class diagrams in UML: inheritance 7-43

44 Case Study for UML Diagrams Lab session Work in StarUML 7-44

45 End of class 7-45